Botnet

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Stacheldraht botnet diagram showing a DDoS attack. (Note this is also an example of a type of client-server model of a botnet.)

A botnet is a number of Internet-connected devices used by a botnet owner to perform various tasks. Botnets can be used to perform Distributed Denial Of Service Attack, steal data, send spam, allow the attacker access to the device and its connection. The owner can control the botnet using command and control (C&C) software.[1] The word botnet is a combination of the words robot and network. The term is usually used with a negative or malicious connotation.

Applications[edit]

Botnets sometimes compromise computers whose security defenses have been breached and control ceded to a third party. Each such compromised device, known as a "bot", is created when a computer is penetrated by software from a malware (malicious software) distribution. The controller of a botnet is able to direct the activities of these compromised computers through communication channels formed by standards-based network protocols such as IRC and Hypertext Transfer Protocol (HTTP).[2]

Botnets are increasingly rented out by cyber criminals as commodities for a variety of purposes.[3]

Architecture[edit]

Botnet architecture has evolved over time in an effort to evade detection and disruption. Traditionally, bot programs are constructed as clients which communicate via existing servers. This allows the bot herder (the person controlling the botnet) to perform all control from a remote location, which obfuscates their traffic.[4] Many recent botnets now rely on existing peer-to-peer networks to communicate. These P2P bot programs perform the same actions as the client-server model, but they do not require a central server to communicate.

Client-server model[edit]

A network based on the client-server model, where individual clients request services and resources from centralized servers

The first botnets on the internet used a client-server model to accomplish their tasks. Typically, these botnets operate through Internet Relay Chat networks, domains, or websites. Infected clients access a predetermined location and await incoming commands from the server. The bot herder sends commands to the server, which relays them to the clients. Clients execute the commands and report their results back to the bot herder.

In the case of IRC botnets, infected clients connect to an infected IRC server and join a channel pre-designated for C&C by the bot herder. The bot herder sends commands to the channel via the IRC server. Each client retrieves the commands and executes them. Clients send messages back to the IRC channel with the results of their actions.[4]

IRC is a historically favored means of C&C because of its communication protocol. A bot herder creates an IRC channel for infected clients to join. Messages sent to the channel are broadcast to all channel members. The bot herder may set the channel's topic to command the botnet. E.g. the message :herder!herder@example.com TOPIC #channel ddos www.victim.com from the bot herder alerts all infected clients belonging to #channel to begin a DDoS attack on the website www.victim.com. An example response :bot1!bot1@compromised.net PRIVMSG #channel I am ddosing www.victim.com by a bot client alerts the bot herder that it has begun the attack.[5]

One problem with using IRC is that each bot client must know the IRC server, port, and channel to be of any use to the botnet. Anti-malware organizations can detect and shut down these servers and channels, effectively halting the botnet attack. If this happens, clients are still infected, but they typically lie dormant since they have no way of receiving instructions.[5] To mitigate this problem, a botnet can consist of several servers or channels. If one of the servers or channels becomes disabled, the botnet simply switches to another. It is still possible to detect and disrupt additional botnet servers or channels by sniffing IRC traffic. A botnet adversary can even potentially gain knowledge of the control scheme and imitate the bot herder by issuing commands correctly.[6]

Many large botnets tend to use domains rather than IRC in their construction (see Rustock botnet and Srizbi botnet). They are usually hosted with bulletproof hosting services.

Peer-to-peer[edit]

A peer-to-peer (P2P) network in which interconnected nodes ("peers") share resources amongst each other without the use of a centralized administrative system

In response to efforts to detect and decapitate IRC botnets, bot herders have begun deploying malware on peer-to-peer networks. These bots may use digital signatures so that only someone with access to the private key can control the botnet.[5] See e.g. Gameover ZeuS and ZeroAccess botnet.

Newer botnets fully operate over P2P networks. Rather than communicate with a centralized server, P2P bots perform as both a command distribution server and a client which receives commands.[7] This avoids having any single point of failure, which is an issue for centralized botnets.

In order to find other infected machines, the bot discreetly probes random IP addresses until it contacts another infected machine. The contacted bot replies with information such as its software version and list of known bots. If one of the bots' version is lower than the other, they will initiate a file transfer to update.[5] This way, each bot grows its list of infected machines and updates itself by periodically communicating to all known bots.

Core components of a botnet[edit]

There are several core components in a botnet which have been used. The main ones are listed below

Command and control[edit]

In the field of computer security, command and control (C&C) infrastructure consists of servers and other technical infrastructure used to control malware in general, and, in particular, botnets. Command and control servers may be either directly controlled by the malware operators, or themselves run on hardware compromised by malware. Fast-flux DNS can be used as a way to make it difficult to track down the control servers, which may change from day to day. Control servers may also hop from DNS domain to DNS domain, with domain generation algorithms being used to create new DNS names for controller servers.

In some cases, computer security experts have succeeded in destroying or subverting malware command and control networks, by, among other means, seizing servers or getting them cut off from the Internet, denying access to domains that were due to be used by malware to contact its C&C infrastructure, and, in some cases, breaking into the C&C network itself. In response to this, C&C operators have resorted to using techniques such as overlaying their C&C networks on other existing benign infrastructure such as IRC or Tor, using peer-to-peer networking systems that are not dependent on any fixed servers, and using public key encryption to defeat attempts to break into or spoof the network.

Zombie computer[edit]

In computer science, a zombie computer is a computer connected to the Internet that has been compromised by a hacker, computer virus or trojan horse and can be used to perform malicious tasks of one sort or another under remote direction. Botnets of zombie computers are often used to spread e-mail spam and launch denial-of-service attacks. Most owners of zombie computers are unaware that their system is being used in this way. Because the owner tends to be unaware, these computers are metaphorically compared to zombies. A coordinated DDoS attack by multiple botnet machines also resembles a zombie horde attack.

Construction[edit]

This example illustrates how a botnet is created and used for malicious gain.

  1. A hacker purchases or builds a Trojan and/or exploit kit and uses it to start infecting users' computers, whose payload is a malicious application—the bot.
  2. The bot on the infected PC logs into a particular command-and-control (C&C) server. (This allows the bot master to keep logs of how many bots are active and online.)
  3. The bot master may then use the bots to gather keystrokes or use form grabbing to steal online credentials and may rent out the botnet as DDoS and/or spam as a service or sell the credentials online for a profit.
  4. Depending on the quality and capability of the bots the value is increased or decreased.

Common features[edit]

  • Most botnets currently feature distributed denial-of-service attacks in which multiple systems submit as many requests as possible to a single Internet computer or service, overloading it and preventing it from servicing legitimate requests. An example is an attack on a victim's server. The victim's server is bombarded with requests by the bots, attempting to connect to the server therefore overloading it.
  • Spyware is software which sends information to its creators about a user's activities – typically passwords, credit card numbers and other information that can be sold on the black market. Compromised machines that are located within a corporate network can be worth more to the bot herder, as they can often gain access to confidential corporate information. Several targeted attacks on large corporations aimed to steal sensitive information, such as the Aurora botnet.[8]
  • E-mail spam are e-mail messages disguised as messages from people, but are either advertising, annoying, or malicious.
  • Click fraud occurs when the user's computer visits websites without the user's awareness to create false web traffic for personal or commercial gain.
  • Bitcoin Mining has been added to some of the more recent botnets have which include bitcoin mining[9] as a feature in order to generate profits for the operator of the botnet.
  • Self spreading functionality, to seek for pre-configured command-and-control(CNC) pushed instruction contains of targeted devices or network, to aim for more infection, is also spotted in several botnet. Some of the botnet is utilizing this function automate its infection.

The botnet controller community features a constant and continuous struggle over who has the most bots, the highest overall bandwidth, and the most "high-quality" infected machines, like university, corporate, and even government machines.[10]

Organization[edit]

While botnets are often named after the malware that created them, multiple botnets typically use the same malware, but are operated by different entities.[11]

A botnet's originator (known as a "bot herder" or "bot master") can control the group remotely, usually through IRC or Domains, and often for criminal purposes. This is known as the command-and-control (C&C). Though rare, more experienced botnet operators program command protocols from scratch. These protocols include a server program, a client program for operation, and the program that embeds the client on the victim's machine. These communicate over a network, using a unique encryption scheme for stealth and protection against detection or intrusion into the botnet.[citation needed]

A bot typically runs hidden and uses a covert channel (e.g. the RFC 1459 (IRC) standard, Twitter, or IM) to communicate with its C&C server. Generally, the perpetrator has compromised multiple systems using various tools (exploits, buffer overflows, as well as others; see also RPC). Newer bots can automatically scan their environment and propagate themselves using vulnerabilities and weak passwords. Generally, the more vulnerabilities a bot can scan and propagate through, the more valuable it becomes to a botnet controller community. The process of stealing computing resources as a result of a system being joined to a "botnet" is sometimes referred to as "scrumping."[citation needed]

To thwart detection, some botnets are scaling back in size. As of 2006, the average size of a network was estimated at 20,000 computers.[12]

Recruitment[edit]

Computers can be co-opted into a botnet when they execute malicious software. This can be accomplished by luring users into making a drive-by download, exploiting web browser vulnerabilities, or by tricking the user into running a Trojan horse program, which may come from an email attachment. This malware will typically install modules that allow the computer to be commanded and controlled by the botnet's operator. After the software is downloaded, it will call home (send a reconnection packet) to the host computer. When the re-connection is made, depending on how it is written, a Trojan may then delete itself, or may remain present to update and maintain the modules. Many computer users are unaware that their computer is infected with bots.[13]

The first botnet was first acknowledged and exposed by Earthlink during a lawsuit with notorious spammer Khan C. Smith[14] in 2001 for the purpose of bulk spam accounting for nearly 25% of all spam at the time.[citation needed]

Countermeasures[edit]

The geographic dispersal of botnets means that each recruit must be individually identified/corralled/repaired and limits the benefits of filtering. Some botnets use free DNS hosting services such as DynDns.org, No-IP.com, and Afraid.org to point a subdomain towards an IRC server that harbors the bots. While these free DNS services do not themselves host attacks, they provide reference points (often hard-coded into the botnet executable). Removing such services can cripple an entire botnet. Some botnets implement custom versions of well-known protocols. The implementation differences can be used for detection of botnets. For example, Mega-D features a slightly modified SMTP protocol implementation for testing spam capability. Bringing down the Mega-D's SMTP server disables the entire pool of bots that rely upon the same SMTP server.[15]

Computer and network security companies have released software to counter botnets. Norton AntiBot was aimed at consumers, but most target enterprises and/or ISPs. Host-based techniques use heuristics to identify bot behavior that has bypassed conventional anti-virus software. Network-based approaches tend to use the techniques described above; shutting down C&C servers, nullrouting DNS entries, or completely shutting down IRC servers. BotHunter is software, developed with support from the U.S. Army Research Office, that detects botnet activity within a network by analysing network traffic and comparing it to patterns characteristic of malicious processes.

Some botnets are capable of detecting and reacting to attempts to investigate them[citation needed], reacting perhaps with a DDoS attack on the IP address of the investigator.

Researchers at Sandia National Laboratories are analyzing botnets' behavior by simultaneously running one million Linux kernels—a similar scale to a botnet—as virtual machines on a 4,480-node high-performance computer cluster to emulate a very large network, allowing them to watch how botnets work and experiment with ways to stop them.[16]

Historical list of botnets[edit]

Date created Date dismantled Name Estimated no. of bots Spam capacity (bn/day) Aliases
1999 !a 999,999,999 100000 !a
2004 (Early) Bagle 230,000[17] 5.7 Beagle, Mitglieder, Lodeight
Marina Botnet 6,215,000[17] 92 Damon Briant, BOB.dc, Cotmonger, Hacktool.Spammer, Kraken
Torpig 180,000[18] Sinowal, Anserin
Storm 160,000[19] 3 Nuwar, Peacomm, Zhelatin
2006 (around) 2011 (March) Rustock 150,000[20] 30 RKRustok, Costrat
Donbot 125,000[21] 0.8 Buzus, Bachsoy
2007 (around) Cutwail 1,500,000[22] 74 Pandex, Mutant (related to: Wigon, Pushdo)
2007 Akbot 1,300,000[23]
2007 (March) 2008 (November) Srizbi 450,000[24] 60 Cbeplay, Exchanger
Lethic 260,000[17] 2 none
2007 (September) dBot 10,000+ (Europe) dentaoBot, d-net, SDBOT
Xarvester 10,000[17] 0.15 Rlsloup, Pixoliz
2008 (around) Sality 1,000,000[25] Sector, Kuku
2008 (around) 2009-Dec Mariposa 12,000,000[26]
2008 (November) Conficker 10,500,000+[27] 10 DownUp, DownAndUp, DownAdUp, Kido
2008 (November) 2010 (March) Waledac 80,000[28] 1.5 Waled, Waledpak
Maazben 50,000[17] 0.5 None
Onewordsub 40,000[29] 1.8
Gheg 30,000[17] 0.24 Tofsee, Mondera
Nucrypt 20,000[29] 5 Loosky, Locksky
Wopla 20,000[29] 0.6 Pokier, Slogger, Cryptic
2008 (around) Asprox 15,000[30] Danmec, Hydraflux
0 Spamthru 12,000[29] 0.35 Spam-DComServ, Covesmer, Xmiler
2008 (around) Gumblar
2009 (May) November 2010 (not complete) BredoLab 30,000,000[31] 3.6 Oficla
2009 (Around) 2012-07-19 Grum 560,000[32] 39.9 Tedroo
Mega-D 509,000[33] 10 Ozdok
Kraken 495,000[34] 9 Kracken
2009 (August) Festi 250,000[35] 2.25 Spamnost
2010 (January) LowSec 11,000+[17] 0.5 LowSecurity, FreeMoney, Ring0.Tools
2010 (around) TDL4 4,500,000[36] TDSS, Alureon
Zeus 3,600,000 (US only)[37] Zbot, PRG, Wsnpoem, Gorhax, Kneber
2010 (Several: 2011, 2012) Kelihos 300,000+ 4 Hlux
2011 or earlier 2015-02 Ramnit 3,000,000[38]
2012 (Around) Chameleon 120,000[39] None
2016 (August) Mirai (malware) 380,000 None
  • Researchers at the University of California, Santa Barbara took control of a botnet that was six times smaller than expected. In some countries, it is common that users change their IP address a few times in one day. Estimating the size of the botnet by the number of IP addresses is often used by researchers, possibly leading to inaccurate assessments.[40]

See also[edit]

References[edit]

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  2. ^ Ramneek, Puri (2003-08-08). "Bots &; Botnet: An Overview" (PDF). SANS Institute. Retrieved 12 November 2013. 
  3. ^ Danchev, Dancho (11 October 2013). "Novice cyberciminals offer commercial access to five mini botnets". Retrieved 28 June 2015. 
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  6. ^ Schiller, Craig A.; Binkley, Jim; Harley, David; Evron, Gadi; Bradley, Tony; Willems, Carsten; Cross, Michael (2007-01-01). Botnets. Burlington: Syngress. pp. 77–95. ISBN 9781597491358. 
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  8. ^ "Operation Aurora — The Command Structure". Damballa.com. Archived from the original on 11 June 2010. Retrieved 30 July 2010. 
  9. ^ "Bitcoin Mining". BitcoinMining.com. Archived from the original on 30 April 2016. Retrieved 30 April 2016. 
  10. ^ "Trojan horse, and Virus FAQ". DSLReports. Retrieved 7 April 2011. 
  11. ^ Many-to-Many Botnet Relationships, Damballa, 8 June 2009.
  12. ^ "Hackers Strengthen Malicious Botnets by Shrinking Them" (PDF). Computer; News Briefs. IEEE Computer Society. April 2006. doi:10.1109/MC.2006.136. Retrieved 12 November 2013. The size of bot networks peaked in mid-2004, with many using more than 100,000 infected machines, according to Mark Sunner, chief technology officer at MessageLabs.The average botnet size is now about 20,000 computers, he said. 
  13. ^ Teresa Dixon Murray. "Banks can't prevent cyber attacks like those hitting PNC, Key, U.S. Bank this week". Cleveland.com. Retrieved 2 September 2014. 
  14. ^ Credeur, Mary. "Atlanta Business Chronicle, Staff Writer". bizjournals.com. Retrieved 22 July 2002. 
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  20. ^ Chuck Miller (2008-07-25). "The Rustock botnet spams again". SC Magazine US. Retrieved 30 July 2010. 
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  22. ^ "Pushdo Botnet — New DDOS attacks on major web sites — Harry Waldron — IT Security". Msmvps.com. 2010-02-02. Retrieved 30 July 2010. 
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  27. ^ "Calculating the Size of the Downadup Outbreak — F-Secure Weblog : News from the Lab". F-secure.com. 2009-01-16. Retrieved 24 April 2010. 
  28. ^ "Waledac botnet 'decimated' by MS takedown". The Register. 2010-03-16. Retrieved 23 April 2011. 
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  35. ^ Kirk, Jeremy (Aug 16, 2012). "Spamhaus Declares Grum Botnet Dead, but Festi Surges". PC World. 
  36. ^ "Cómo detectar y borrar el rootkit TDL4 (TDSS/Alureon)". kasperskytienda.es. 2011-07-03. Retrieved 11 July 2011. 
  37. ^ "America's 10 most wanted botnets". Networkworld.com. 2009-07-22. Retrieved 10 November 2011. 
  38. ^ http://phys.org/news/2015-02-eu-police-malicious-network.html
  39. ^ "Discovered: Botnet Costing Display Advertisers over Six Million Dollars per Month". Spider.io. 2013-03-19. Retrieved 21 March 2013. 
  40. ^ Espiner, Tom (2011-03-08). "Botnet size may be exaggerated, says Enisa | Security Threats | ZDNet UK". Zdnet.com. Retrieved 10 November 2011. 

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